1. Field of the Invention
The present invention relates to the field of chemical mechanical polishing. More particularly, the present invention relates to methods and apparatus that allow for chemical mechanical polishing using a flexible pad and variable fluid flow for variable polishing.
2. Description of the Related Art
Chemical mechanical polishing (CMP) of materials for VLSI and ULSI applications has important and broad application in the semiconductor industry. CMP is a semiconductor wafer flattening and polishing process that combines chemical removal of layers such as insulators, metals, and photoresists with mechanical polishing or buffing of a wafer layer surface. CMP is generally used to flatten surfaces during the wafer fabrication process, and is a process that provides global planarization of the wafer surface. For example, during the wafer fabrication process, CMP is often used to flatten/polish the profiles that build up in multilevel metal interconnection schemes. Achieving the desired flatness of the wafer surface must take place without contaminating the desired surface. Also, the CMP process must avoid polishing away portions of the functioning circuit parts.
U.S. Pat. No. 6,103,628, assigned to the assignee of the present invention, describes a reverse linear chemical mechanical polisher that operates to use a reverse linear motion to perform chemical mechanical polishing. In use, a rotating wafer carrier within a polishing region holds the wafer being polished.
U.S. patent application Ser. No. 09/684,059, filed Oct. 6, 2000 and which is a continuation-in-part of U.S. Pat. No. 6,103,628, describes various features of a reverse linear chemical mechanical polisher, including a platen support in the polishing region that uses a fluid such as air or magnetic films to levitate the polishing pad off of the platen support while the pad moves with reverse linear motion at the desired speed above the platen support.
In a linear polisher, U.S. Pat. No. 5,916,012 describes using a support housing that underlies an endless loop belt and to which a polishing pad is attached on the outer surface of the endless loop belt, with the support housing including a plurality of openings for dispensing a pressurized fluid. These openings are configured into different concentric and pie-shaped groupings that can each be separately and independently controlled in order to apply a different amount of pressurized fluid to corresponding portions of the polishing pad. The endless loop belt, as actually implemented in practice, was made of stainless steel, to which an adhesive was applied to allow a polishing material to attach thereto. In operation, although the pressurized fluid can be varied with respect to the various concentric and pie-shaped concentric groupings, the rigidity of the stainless steel inner endless loop prevents the ejected pressurized fluid from significantly impacting the polishing effect at a particular location of the wafer being polished. While certain localized pressure variations may have been possible when practicing the '012 patent, the local control that may have been achievable was still not sufficiently localized to correct for variations that occur millimeters apart.
The present inventors have determined, however, that it would be advantageous to provide for a reverse linear polisher that uses a flexible and relatively light polishing pad and variable fluid flow for polishing of a wafer in order to control the polishing profile at various locations on the wafer. Accordingly, further improvements as described herein are described.